# Work done by friction opposing a force at an angle

Let's imagine there's a block of mass m sitting on a rough surface with a kinetic friction coefficient $\mu$. It's being pulled with a constant force $A$ at $h$ degrees above the horizontal and is displaced a distance $d$. The work done by $A$ on the block is positive and is the horizontal component of $A$ times the displacement:

$$A\cos (h)*d.$$

I thought this meant that the work done by friction would be either the negative of that amount or else

$$\mu*(mg-A\sin (h))*d$$

but apparently not?

• What does it mean if the force and the displacement are in opposite directions? – BowlOfRed Oct 23 '15 at 5:07
• It means the work done is negative. – AaronF Oct 23 '15 at 14:06